Login to your Office 365 tenant and navigate to the Admin Console page, click on Users and then Active Users. From there click Active Directory Sync Set Up
You will then be faced with 7 options, click on option 3 Active Directory Synchronization and click on Active.
You will be asked to confirm you want to ensure Active Directory sync, click Yes.
As I am doing this in a brand new Active Directory I did not bother running the IdFix Tool, but if you are running this in your production Active Directory that may need checking you should run this tool.
Stage 5 requires you to download the Azure AD Dir Sync tool, click Download and it will start, the download is around 200MB's.
Once the Dir Sync tool has downloaded, double click on the exe file to run the setup. Click Next.
Accept the License Terms and click Next.
The Dir Sync wizard will then begin installing the required components.
Choose to start the configuration wizard.
Enter the credentials you used to configure your Office tenant.
Now local domain credentials are required.
Do not choose to configure a Hybrid Deployment.
Ensure you choose to configure Password Sync as this will be a good fall back if your AD FS infrastructure fails, if DirSync is configured to sync passwords users will still be able to login to Office 365 using their domain credentials.
Kick off a sync job and click Finish.
To test the users have been synced to the Office 365 tenant check with in the console.